The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As is known in itself, it is generally suitable to provide an exhaust cone/primary nozzle assembly at the rear of an aircraft turbojet engine, so as to optimize the flow of the hot gasses expelled by the turbojet engine on the one hand, and to absorb at least some of the noise created by the interaction of those hot gasses with the ambient air and with the cold air flow expelled by the fan of the turbojet engine on the other hand.
These elements are commonly referred to as a “cone” and a “nozzle” or “primary nozzle”.
One such traditional exhaust cone 1 is shown in FIG. 1 appended hereto, on which the front and rear of the structure along an engine axis are situated on the left and right sides of the figure, respectively.
This exhaust cone is intended to be positioned downstream from the turbine of the turbojet engine, above which the primary nozzle is placed concentrically. The exhaust cone and the primary nozzle are both fastened on a casing of the turbojet engine by a flange fastening system.
More specifically, the exhaust cone 1 comprises, strictly speaking, a front part 5 (commonly called the “front cone”), which is substantially cylindrical, and a rear part 7 (commonly called the “rear cone”), which is conical.
The front part 5 can in particular be acoustic or stiffened monolithic.
If the first part 5 is acoustic, that means that it comprises at least one peripheral sound attenuation structure of the sandwich type comprising at least one resonator, in particular of the honeycomb type, covered by a perforated outer skin and a solid inner skin.
The outer skin also constitutes an outer surface (sheet) of the front part 5 of the exhaust cone.
If the front part 5 is stiffened monolithic, that means that the structure is made up of a single sheet reinforced by stiffeners.
The rear part 7 is monolithic and stiffened by stiffeners 9d. 
The front part 5 and the rear part 7 of the exhaust cone may in particular be made from sheets of metal alloy of the Inconel 625 type and may be assembled using a flange junction system denoted 9b for the front flange part and 9c for the rear flange part.
The front part 5 further comprises an upstream connecting flange 9a designed to allow it to be attached to the rear of the turbojet engine.
FIG. 2 shows that, traditionally, the flange 9b of the front part 5 has a part 11 with a diameter substantially equal to that of the outer skin of said front part 5 on the one hand, and a part 13 with a diameter smaller than that of the flange 9c of the rear part 7 to which it is designed to be connected, such that said part 13 of the flange 9b can be inserted inside the flange 9c of the rear part 7, on the other hand.
Housings 15 formed in the thickness of the flange 9c make it possible to receive bolts 17 passing through said flange 9c and the flange 9b, fastened using nuts 18 attached through the inside of the exhaust cone 1 thus assembled.
The housings 15 make it possible to prevent the heads 19 of the bolts 17 from protruding toward the outside of the cone 1, and thus do not cause aerodynamic losses.
As can be understood in light of the preceding, an exhaust cone of the prior art (FIG. 2) is a complex structure, involving many parts, and has a high manufacturing cost and affects the mass of the assembly, which is not desirable.
There is therefore a constant need to simplify the assembly structure of such an exhaust cone, so as to reduce both the mass and manufacturing cost thereof.
In particular, according to the prior art, if the front part is of the acoustic type, the acoustic panel is closed at its front and rear ends, respectively, by peripheral flanges having a C-shaped section and commonly called closing Cs.
These closing Cs are connected, in particular by brazing, to the corresponding front and rear flanges respectively providing the connection with the turbojet engine and the rear cone part and provide a large portion of the maintenance of the sound attenuation structure.
These closing Cs are expensive parts made by machining, and above all they represent a non-negligible mass relative to the total mass of the exhaust cone.